A mutant of escherichia coli defective in removing 3' terminal nucleotides from some transfer RNA precursor molecules.

The conversion of precursor RNA into bacteriophage T4 proline and serine transfer RNAs includes two steps for the enzymatic removal of nucleotides from the 3' ends of RNA chains. Neither of these steps occur following infection of a mutant of Escherichia coli that was previously shown to block the suppressor function of T4 serine transfer RNA. Cell-free extracts of this mutant are furthermore deficient in a wild type enzyme activity that removes nucleotides from the 3' ends of one of the RNA chains described above. The relation of this enzyme to other 3' ribonucleases is not known. We subsequently examined the mutant for its ability to support the biosynthesis of other bacteriophage transfer RNAs. In one instance that is analogous to the proline-serine precursor RNA, maturation of the precursor RNA was blocked during infection of mutant cells. In another instance, precursor RNA maturation was normal, even though this involved the removal of 3'nucleotides. These observations point to the possible existence of at least two 3' ribonucleases for the biosynthesis of transfer RNAs.